The present invention relates to thermal spray systems for deposition of high quality coatings.
Different thermal spraying methods, such as, flame spraying (including high-velocity oxy-fuel (H.V.O.F.) thermal spray devices, and high-velocity air-fuel (H.V.A.F.) thermal spray devices), plasma spraying, and electric arc spraying, have been used to coat metallic or other surfaces. A flame spray device deposits typically metals, ceramics, or cermet types of materials onto a substrate. The flame spray device includes a combustion chamber that receives a mixture of fuel (e.g., propylene or propane) and oxidant (e.g., oxygen or air) in the form of a pressurized gas and generates in a combustion reaction a high-temperature, high-pressure combustion stream. The device directs the combustion stream from the combustion chamber into a flow nozzle. The spray material (e.g., a powder, a solid rod or wire) is introduced into the high-velocity combustion stream, which at least partially melts the material. The combustion stream also "atomizes" the melted of softened material and propels it to the target substrate. Depending on the design, different devices can accelerate the particle stream up to supersonic velocities or hypersonic velocities (i.e., velocities equal to several times the velocity of sound). The supersonic particle stream may be generated by a single stage combustion device or two stage combustion device or by a device that produces steady-state continuous detonations.
A plasma spray device generates and emits a high-velocity, high-temperature gas plasma delivering a powdered or particulate material onto a substrate. The device forms the gas plasma by flowing a gas through an electric arc in the nozzle of a spray gun, causing the gas to ionize into a plasma stream. The spray material, which may be preheated, is introduced in the plasma stream. The particle-plasma stream, which can be accelerated up to a hypersonic velocity, is directed to the substrate. While plasma spraying can produce good quality coatings, the device is relatively complex and expensive.
An arc spray device generates an electric arc zone between two consumable wire electrodes, which may be solid or composite wires. As the electrodes melt, the device continuously feeds the electrode wires into the arc zone and also blasts a compressed gas into the zone to break and "atomize" the molten material. The compressed gas propels the atomized material and directs it to the substrate to form a coating. Alternatively, an arc spray device can use non-consumable electrodes and introduce powder into the heated gas.